Assuming you have an AirPlay compatible H.264 video file with no audio ...

Pull your stems into Compressor using the Add Surround Sound Option. Use the AC3 file preset. Use Coding Mode:

3/2 (L,C,R,LS,RS). Enable LFE.

Now have Compressor build the file.

Next use Quicktime 7 to open the H.264 video and the encoded AC3 audio file. Make sure you queue the movie file and the audio file at the beginning. Select the audio file window - from menu:Edit/Select All/Copy.

Now select the movie window - from menu:Edit/Add to Movie

Now check Show Movie Properties from the QT 7 menu. You should see the AC3 audio track with the proper channel routing. Save it out. That should do it ...

Would someone explain what stems are? (I know that in the old days working with 7 and Soundtrack Pro, that the result would be STEMS) but I confess I don't really know what I'm looking at when I see them.
(A google search first page talked a lot about plants, florists and branches)

From the viewpoint of audio deliverables for broadcast the term stem specifically applies to the separate elements that make up the mix. Music, Narration, Dialog and Effects are considered the typical stems. They can be mono, stereo , 5.1 or 7.1 . The term really means mix components and is not used to describe the mix or DME. When I hear people describing Roles as stems I cringe as roles best describe routing - bussing or sub grouping as it is described in the DAW world.

Sometimes I am asked to split the effects stems further into foley, atmos & sync fx. Nat Geo like this further stem split. The stem files are delivered as wavs and not usually part of a quicktime file or HDCamSR tape as basic stems need 4 x 6 channels. That on top of full mix 5.1, mix stereo, DME 5.1 & stereo adds up to 48 channels.

To your question Jeremy I use Avidemux(GTK+) software to mux the ac3 to any file. So there is no recompression or format change. This is free Linux software and it enables me to remove an existing audio track and remux any other audio track including ac3. I have subler but haven't used it since finding Avidemux. It is much like Quicktime Pro but works for mp4 and lots of other formats.

[Michael Gissing]"To your question Jeremy I use Avidemux(GTK+) software to mux the ac3 to any file. So there is no recompression or format change. This is free Linux software and it enables me to remove an existing audio track and remux any other audio track including ac3"

Thanks, Michael.

It's sounds just like Subler. As far as I can tell, there's no format change there either, besides the wrapper. Is that right?

Every video player on the planet should be able to do a standard foldown from 5.1 to stereo so the ac3 should work regardless. Otherwise the risk is the player will not be able to chose or will try to play both audio streams and mix them.

A good player like VLC should allow the user to chose the appropriate track but that doesn't make it idiot proof as the operator will need some knowledge.

I've done these easily in FCPX - just using a 5.1 project and making certain all my roles and audio properties are correct - i.e Dialog set to Center Channel etc. and used the Apple TV 1080p Share with 5.1 - works perfect via Airplay to Apple TV!

[Lance Bachelder]"I've done these easily in FCPX - just using a 5.1 project and making certain all my roles and audio properties are correct - i.e Dialog set to Center Channel etc. and used the Apple TV 1080p Share with 5.1 - works perfect via Airplay to Apple TV!"

When I do this, it says that it is going to create a stereo file in the export dialog like this:

In QT7, I get back a stereo report like this:

I can only get Surround if I choose Master file and change the codec from Source to h264.

oh god yes. Mine was late last minute with the pro tools lady kept to check the output. PPro will actually clean pass through and output a 5.1 though. As ever depends on the sequence setup thing. You can't monitor it without a track submix for preview mind you. I'm a moron on audio but you can actually get fond of the track mixer apparatus. lots of things going on there?

aside from that tho - the basic inability to set source monitor audio db that carries through onto the timeline? You what?
(you only get a one off +- gain dialogue box thing? Doesn't carry through? surely not kids.)

Or I'm stupid on that. I'm poking at it. Also absolutely no audio source keyframing represented.
Audio source seems a bit of a wasteland.

[Aindreas Gallagher]"You can't monitor it without a track submix for preview mind you."

But it doesn't always work. I can't mix down an 8 channel output sequence to stereo monitoring and keep any sort of channel assignments, for instance. This is one of the things I loved about FCP7 is that you could map any track at any time to any output channel. Pr forces a new sequence, setup just right, with really crappy mapping. If I want an 8 channel output, monitored in stereo, there aren't enough submixes in the world to get it done as every time I switch back from the submix, my output channel assignments are blown. Then I have to remap and delete the submix.

It drives me nuts. I do like the idea of the submix system (media 100 had it over 10 years ago when I used it), but it doesn't work like a submix on a real live audio mixer works. I am far from an audio expert, I just know how I want things to work.

The "down mix" button in FCP7 was a very elegant solution.

[Aindreas Gallagher]"aside from that tho - the basic inability to set source monitor audio db that carries through onto the timeline? You what? "

I skimmed through the rest of the replies, and don't think you've got this answered yet. Export your 5.1 master ProRes file from your fcpx timeline. Open it in QT to make sure that it is indeed 5.1 in metadata.

Download Handbrake (and VLC). Handbrake started reading ProRes files a while back. I imagine the decode is going to 8 bit, but the resulting h.264 is anyway, so don't worry.

Grab the AppleTV3 preset and then modify the audio settings to just make the one AC3 5.1 track.

The x.264 encoder in handbrake is ridiculously good compared to just about every paid transcoder out there and the audio will be 5.1.

Not to talk bad on episode, but even if you do get the pro audio option, you have to use the channel mapper to rearrange audio into the order they expect (which by the way matches no industry standard).

I had read about using handbrake for this, and I have handbrake, but I have never really been truly impressed with handbrakes results. Perhaps I'm holding it wrong and I'll give it another shot. It won't read 5.1 from FCP7 (due to the channels being 1 stereo, 2 mono, and 1 stereo despite having the channel assignments in the correct order), but an FCPX surrounded export does provide the proper metadata to handbrake (5.1).

If this does work, though, it will be nice as it's one step instead of a three step Subler workflow.

[Keith Koby]"Not to talk bad on episode, but even if you do get the pro audio option, you have to use the channel mapper to rearrange audio into the order they expect (which by the way matches no industry standard)."

1 to 2
2 to 3
3 to 1
4 to 6
5 to 4
6 to 5

Because of all the testing, it is now committed to memory, or rather, an episode preset ;)

Thanks so much, Keith. I'll post back about handbrake results. Much appreciated.